On highway trucks often have a power-take-off ("PTO") or other device which allows the truck engine to power devices connected to the truck. The PTO generally includes a rotating shaft extending rearwardly from the cab. The device to be powered is then connected to the PTO shaft. As the PTO shaft rotates, power is transmitted to the device. One such device is a refrigerated trailer. In some refrigerated trailers the PTO is used to power the compressor to keep the trailer at the desired refrigerated temperature. Other vehicles that have a PTO include utility vehicles, school buses and firetrucks.
Thus, the truck engine provides power to both the PTO and the drive train of the truck. In cases where the truck is travelling on the road, the engine speed is generally high enough to provide sufficient power for both the PTO and the transmission. However, when the truck is parked and idling, the engine may not produce sufficient power to drive the external device connected to the PTO. In this instance, the operator is required to press the accelerator pedal to elevate the idle speed to cause the engine to produce more power. However, manually maintaining a desired elevated idle speed is inefficient and prevents the operator from sleeping or performing other tasks when the truck is stopped and idling.
It would be preferable to use a truck engine having an automatic means for selectively commanding an elevated idle level at desired times.